This invention relates to phase detectors and more particularly to an improved phase detector suitable for use in a television and other receiver systems.
Some contemporary television systems, for example, Secam television systems, utilize a gated phase detector in conjunction with the identification line burst and frame identification signals for proper synchronization. As will be explained, some contemporary gated phase detectors produce an output error current which can be comparable in magnitude with the desired output current unless strict tolerances of the circuit components are maintained. If the gated phase detector is fabricated in integrated circuit form the tight tolerances cannot be maintained in production.
For example, with reference to the aforementioned Secam identification scheme a gated phase detector circuit as shown in FIG. 1 herein must be gated on for periods encompassing the television line bursts and the frame identification signals. Due to system tolerances it has been found that the cumulative gating period will be two to three times the cumulative duration of the line bursts. Therefore, contemporary phase detector circuits comprising a differential amplifier and current mirror circuitry require bias currents of sufficient magnitude to handle noise signals of up to ten times the discriminator output supplied thereto during the television line bursts. Hence, the output error current, for instance, the error which is generated by the current mirror circuit will become comparable with the desired output current unless the current mirror be exceptionally precise. A three percent error in the currents generated by current mirror circuit tolerance has been found to generate an error output signal equal to the desired output level from the phase detector. Thus, there is a need for a phase detector which overcomes the foregoing problems without requiring precisely matched components or adjustments and which is suitable for fabrication in integrated circuit form.
In view of the above, it is one aspect of the present invention to provide an improved phase detector circuit for producing an output signal in response to input signals applied thereto having little or no error components without requiring precisely matched components.
Another aspect of the invention is to provide a phase detector circuit suitable for fabrication in integrated circuit form comprising an input differential amplifier, a multiplier section and a current mirror circuit for providing an output signal wherein error signals generated due to tolerances of components therein is reduced without requiring precise matching of the components.